As conventional elastic yarns, polyurethane elastic yarns and polyetherester elastic yarns are well known. These conventional elastic yarns have a problem that when a fabric is formed from a single type of elastic yarn, the resultant fabric exhibits an insufficient bulkiness and an unsatisfactory handling property. As means for solving the problem, it is known that the above-mentioned elastic yarn and a low elongation yarn having an ultimate elongation of 40% or less are used to provide a covering yarn in which the low elongation yarn is wound around the elastic yarn, a doubled and twisted yarn of the elastic yarn with the low elongation yarn, a mixed fiber yarn in which the elastic yarn is located in a core portion and the low elongation yarn is arranged in a sheath portion around the core portion, or a composite false-twisted yarn prepared by applying a false-twisting treatment to the mixed fiber yarn. For example, Japanese Unexamined Patent Publication No. 03-174,043 discloses a composite textured stretch yarn having a core portion formed from a block copolymerized polyetherpolyester elastic yarn constituted from hard segments comprising a polybutylene terephthalate polyester and soft segments comprising a polyoxybutyleneglycol polyether, and an outer layer portion (sheath portion) formed from a non-elastic, thermoplastic polymer multifilament yarn.
The above-mentioned conventional composite yarns have excellent stretchability. However, these conventional composite yarns are unsatisfactory in soft hand and color density-increasing (bathochromatic) effect, in practice. Thus, the enhancement of the above-mentioned properties and effect of the composite yarn is desired.